High-frequency receiver



Oct. 23, 1945. I v G. GIYOUNG 2,337,632

HIGH'FREQUENCY RECEIVER Filed March 28, 1944 2. "5 6 I I I RFAHPLIFIER IF 7 AND I f CONVERTER DETECTOR AUDIO AMPLIFIER RECEIVER AUDIO OUTPUT INPUT T0 ANTENNA DURINGTELEGRAPHIC RECEPTION I InQentor:

George G.You by 7 fjwyi H is Attorney.-

Patented Oct. 23, 1945 HIGH-FREQUENCY RECEIVER George G. Young, Bridgeport, Conn, assignor to General Electric Com New York pany, a corporation of Application March 28, 1944, Serial No. 528,421

Claims. '(o1.250-s) My invention relates to high frequency receivers and particularly to receivers adapted for telegraphic reception.

Frequently such receivers are adapted for either telegraphic continuous wave reception or telephonic reception. During telegraphic reception the received oscillations are combined with locally generated oscillations to produce a beat note which may be heard from a suitable reproducing device, such as headphones or loudspeaker. During such telegraphic reception the sensitivity of the receiver is likely to be greater than during telephonic reception with the result that the noise level, which may be tolerated during telephonic reception, may be intolerably high during the telegraphic reception.

An object of my invention is to provide improved means automatically to reduce the sensitivity of the receiver during telegraphic reception.

Another object of my invention is to provide improved means-to couple the local oscillator with the circuits on which the received oscillations appear to produce the desired beat note.

Another object of my invention is to provide such improved coupling of such character that the intensity of the beat note never reduces in response to increase in the intensity of the received oscillations in any part of the range of intensities over which the received signal varies.

The novel features which I believe to be characteristic of my invention are set-"forth with particularity in the appended claims. My invention-itself, however, both as to its organization and; method of operation, together with further objects and advantages thereof, may best be understood by reference to the following descriptionta'ken in connection with the accompanying drawing in which Fig. 1 represents an embodimentof my invention and Fig. 2 represents a characteristic of its operation.

- Referringto Fig. 1 of the drawing, I have shown therein aradio receiver having an antenna I, a radio frequency amplifier and converter 2, an intermediate frequency amplifier 3, a further intermediate frequency amplifier 4, a detector 5, an audiofr'equency amplifier 6, and a suitable signal reproducing device 1, such asheadphones or'a loudspeaker;

a The apparatus! comprises the usual radio frequency portion of the receiver, which may be of superheterodyne type employing a radio frequency amplifiertunable over a band of frequencies in unison witha local oscillator which beats with the received oscillations to produce an intermediate frequency which is constant for all frequencies to be received. This intermediate frequency is amplified by theamplifiers 3 and 4 and supplied to the detector 5; During telephonic reception such oscillations are modulated with the voice and the voice waves are reproduced in the output of the detector, amplified by the audio amplifier 6, and reproduced by thesignal device 1. During telegraphic reception the intermediate frequency wave is not so modulated and to render it audible it is combined with oscillations generated by a further local oscillator 8 inthe amplifier 4 to produce at the output of the detector a beat note having a frequency of, for example, 1,000 cycles, which is reproduced by the signal devicel.

The amplifier 4 is conventionally shown as one having an anode 9 connected through a tuned circuit In and resistance H to the positive side of a source of operating potential, not shown but the terminals of which are indicated at l2. This source may be of any of the usual types and is commonly shunted by a bleeder circuit 153 and a smoothing condenser [4. This amplifier 9 also has a cathode which is connected to ground through the usual bias resistance l5 shunted by a bypass condenser l6. This amplifier also has a control electrode "and, if desired, additional electrodes interposed between this control electrode and the anode such as the ordinary screen and suppressor grids commonly employed in such devices.

The local oscillator 8 likewise comprises an anode l-9, a cathode 22, and a number of grids interposed therebetween including a screen grid 35 which is connected in ground through a by: pass condenser 42. The first grid 23, that is, the one adjacent the cathode, is connected through a grid condenser to one terminal of a frequency determining oscillatory circuit 25. The second. and fourth, or screen, grids are connected through a resistance 26 to the-positive terminal l2 of the source of operating potential, and the remaining grids and the anode H! are connected to ground. 4 The control "electrode 23, in addition to the connection previously described, is connected through a resistance 21 and a further resistance 28 to ground, the latter resistance being shunted by a condenser 29. The cathode 22 is connected to an intermediate point on the inductance 30 of oscillating circuit 25, the lower terminal of which is connected to 'a point 3l' on a bleeder circuit 13 phonic reception the switch 34 is: open and the.

electron discharge oscillator 8 is inoperative. The receiver is thus adapted for telephonic reception. The device 8 is rendered inoperative by the fact that its cathode 22 is connected to the point 3| on the bleeder circuit. which is sufficiently positive with respect to ground and with respect.

to the potential of the control electrode 23 to interrupt the production of oscillations.

When it is desired to receive telegraphic signals switch 34 is closed. This lowers the potential of cathode 22 to ground potential and thus reduces the negative bias between cathode 22 and control electrode 23' and permits the device to oscillate, the electrode 23' acting as a control electrode and its next adjacent electrode 35' actin? as an anode. These oscillations appear across circuit 25 and on resistance 28 and con. denser 2'9 and during the positive peaks thereof produce grid current which also flows through resistances. 21 and 28 producing thereon a negative. bias potential by ordinary grid leak and condenser action. The portion of th s unidirectional potential? which appears on resistance 28- and the; oscillations of the local oscillator frequency-- which appear thereon are supplied through resistance 4| to' the control electrode H of the-amplifier whereby these locally generated oscillations are combined with the intermediate frequency oscillations of the receiver'to produce a beat note in the output of the detector which may be heardfrom the headphones 1. The

tuned circuit l0, and, if desired, additional tuned circuits such as the input to'thedetector 5. prevents harmonic. frequencies'of the local oscillator a 8-from beingeffective in the detector to produce undesired oscillations. The unidirectionalpotential. on resistance 28 operates to increase the negative bias which is-presentbetween the oathodeof the amplifier 4 and control electrode I! y reason. ofthe cathode bias resistance [5 and.

condenser [6 thereby reducing the amplification of this amplifier and hence the sensitivity of the. receiver to reduce the noise level present in the signal device.

That is, commonly in such receivers the sensitivity of the receiver is greater during. the: reception of telegraphic signals than during the reception of telephonic signals with the result. that the noise level maybe excessive during telegraphic reception whereas it may not be excessive during telephonic reception. In accord with my invention, when the oscillator 8 is rend'ered operative by closing switch 34', bias voltage produced on resistance 28 drives the grid l1 additionally negative thereby reducing the amplification of this amplifier and hence reducing the sensitivity: of the receiver and reducing the undesired noise level.

Condenser 29- isv connected'in shunt to resistance 28 and is a value such as to limit the oscillatoryvoltage at grid I! to a desired value and independently of the unidirectional bias voltage supplied from: resistance28 to electrode I1.

In Fig. 2I have: represented the. relation between the receiver" audio output as heard from theloudspeaker 1 plotted asv ordinates against:

negative slope in the curve illustrated in Fig. 2.

This is because such negative slope would mean that the intensity of signal heard in the head- 1 phones decreases while the signal intensity in the antenna increases. Such effect might deceive the operator into believing that he is traveling away from the; station from which he is receiving signals whereas in fact he is approaching it. I have found that with the coupling here described this undesired effect is avoided and that the desired characteristic illustrated in. Fla. 2 is obtained. In addition, it isobtained the.

very simple expedient employed. in the. coupling meansdescribed in connection with 1'. The.

amount of local oscillator voltage. supplied. resistance. 28. to the input of. amplifierv 4 is very small yet very satisfactory. Telegraphic. reoep tion is had. for ignals varying, over. a very wide range. of intensities, as'fIOm two, voltsat antenna. I down. to a few microvolts. This results from the fact that this voltage. is amplified by inter'- d at f equ cy amplifi r be ore. it is ap= plied to detector 5 to beat. with the intermediate. frequency oscillations. i

It will also be noted that the conductor 48 of Fig. 1 leading to the switch. 34 may be .at comparatively low potential so that it may comprise one of the conductors of a multi-conductor cab e leading to a remote point; as in an aircraft. It;

includes the choke coil 33 located at the receiver to prevent the transmission of oscillations produced by the oscillator 8 into the cable. While I have illustrated a particular embodilment of my invention, it will of course be understood that I do not wish to be limited thereto since various modifications both in the circuit arrangement and in the instrumentalities employed be made, and I contemplate by the ap-' pended claims to cover any such modifications asfall within the true spirit and scope of my invention. I I

What I claim as new' and" desire to secure by Letters Patent of the United States; is: g g I. The combination, in a high frequency receiver constructed and arranged for both modulated continuous wave reception and for telegraphic continuous wave reception and having sensitivity sufficiently 'great during sai'd'ftelegraphic reception to produce undesired noise response, of a. local oscillator, means to' beat the oscillations produced by said local oscillator with received oscillations to produce: a beat note duringreception' of telegraphic pulses; means to render said oscillator alternatively operative andfinoperative in accordwith the type. of recept on desired, and means responsive tooperation ofrsaid. local oscillator to reduce the sensitivity of said receiver thereby to reduce: said noise; response.

2. The combination, in a high' frequency re! ceiver'constructed and arranged for. both modulated continuous wave reception and, for tele'a graphic continuous wave reception and" having sensitivity sufilciently' great. during said. 17618:! graphic. receptionto; produce; undesired! noise res spouse, of a local oscillator comprising an electron discharge device having an anode, a cathode, a control electrode, an oscillatory circuit coupled regeneratively to said .anode, cathode and control electrode, a grid leak and condenser connected between said control electrode and cathode, means to render said oscillator alternatively operative and inoperative in accord with the type of reception desired, means to beat the oscillations produced by said oscillator with received oscillations to produce a beat note during reception of telegraphic signals, and means responsive to voltage on said grid leak and condenser to reduce the sensitivity of said receiver during said telegraphic reception thereby to reduce said noise response.

3. The combination, in a high frequency receiver constructed and arranged for both modulated continuous wave reception and for telegraphic continuouswave reception and having sensitivity sufiiciently great during said telegraphic reception to produce undesired noise response, of a local electron discharge oscillator having a control electrode in which current flows during operation, means to render said oscillator alternatively operative and inoperative in accord with the type of reception desired, means to beat the oscillations produced by said oscillator with received oscillations to produce a beat note during reception of telegraphic signals, and means responsive to current in said control electrode to reduce the sensitivity of said receiver during telegraphic reception to reduce said noise re- .sponse.

4. The combination, in a high frequency recuits coupling said electrodes to produce oscillations of frequency diflerent from the frequencyof oscillations amplified by said amplifier by an audible amount, means to render said oscillator cathode of said amplifier to produce said beat note and to reduce the sensitivity of said receiver during operation of said local oscillator.

5. The combination, in a high frequency receiver, of a radio frequency amplifier having a' cathode, a control electrode, and an output circuit, a local electron discharge oscillator having a control electrode, a cathode, and an anode, circuits coupling said electrodes to produce oscillations of frequency different from the frequency of oscillations amplified by said amplifier by an audible amount, means to render said oscillator alternatively operative and inoperative,

and a parallel combination of resistance and capacitance having points spaced apart thereon connected to said control electrodes and to said cathodes respectively whereby unidirectional potential exists between said points during operation of said oscillator and also oscillations of the frequency of said oscillator, said unidirectional potential reducing the sensitivity of said receiver and said oscillations combining with received oscillations to produce said beat note in said output of said amplifier whereby reduction in intensity of said beat note with rise in intensity of received oscillations is avoided.

GEORGE G. YOUNG. 

